> If we're all broke/starving/being exterminated, who will the rich sell to?

Themselves. The economy is a big cycle where money changes hands to drive production i.e. things getting made. AI will simultaneously greatly increase production (especially once humanoid robots are as dexterous as humans) and make the humans whose jobs it will do economically irrelevant.

So the rich will buy and sell very nice things to each other while the rest of us get left out in the cold because we simply cannot compete with the robots. And because they will capture and control all resources (either by law or by force) we won't be able to create a functioning parallel economy either.